1. Field of Invention
The present invention relates to a method of treating a surface of a mold. More specifically, the present invention is directed to a method of forming a carbon film that covers the surface of a mold.
2. Description of Related Art
A technique that uses a mold to produce products with the same shape and quality in a large quantity is known. Japanese Patent Application Publication No. 2008-105082 (JP-A-2008-105082) describes covering the surface of a mold with a carbon film so that the molded product may be easily released from the mold. JP-A-2008-105082 describes covering the surface of a mold with fibrous nanocarbons to improve abrasion resistance, corrosion resistance, thermal conductivity, friction properties and mechanical strength of the surface. Using this technique, on a casting mold, for example, a melt is less likely to stick to the casting mold so that the service life of the casting mold may be increased. In JP-A-2008-105082, carbon nanocoils, carbon nanotubes and carbon nanofilaments are cited as examples of the nanocarbons. They are classified into crystalline carbons.
According to the technique that is described in JP-A-2008-105082, separation of the carbon film from the mold surface may be prevented by the anchor effect of the fibrous nanocarbons. With such an anchor effect of the nanocarbon alone, however, the carbon film is liable to be separated from the mold surface when the production (casting) process using the mold is repeatedly carried out. JP-A-2008-105082 describes that the separation of the carbon film from the mold may be suppressed when a nitride layer or the like is provided between the carbon film and the mold surface. With such a method, however, cracking of nitride layer or separation of the carbon film from the nitride layer inevitably occurs when the production process is repeated. When the carbon film separates from the mold, it is necessary to conduct a maintenance operation to provide a carbon film again. Thus, a need exists for a technique by which separation between the carbon film and the mold can be prevented and the service life of the mold can be further improved.